The design of optical transmission schemes for transmitting the output of a light source through light guides, light pipes, or optical fibers, has as its principle aim, the optimization of light collection efficiency at the light source and the subsequent coupling of such light output to the light distribution medium with as little light loss as possible. Given that the light output from the light source generally spreads out in a spherically radiating manner; that is, at a large angle from the source, one might consider that the optimum approach for collecting such light output for distribution would be to partially surround such light source with a somewhat equally spherically shaped collecting device such as a reflector for instance. One such example of a reflector used to collect the light output of a light source can be found in U.S. Pat. No. 4,811,172 issued to Davenport et al. on Mar. 7, 1989 and assigned to the same assignee as the present invention. Though this approach has demonstrated an improved efficiency in coupling an amount of light output to a bundle of optical fibers for distribution to locations remote from the light source, the use of such a reflector, light source arrangement experiences an inherent limitation to the level of improvement in efficiency. Specifically, because there is a measurable distance between the light source and the reflector, there is some opportunity for the light to be lost or scattered. Additionally, absent a total internal reflection arrangement, in a light collecting or directing arrangement which utilizes a principally reflecting scheme, it is known that some of the light rays will be reflected more than once which has the inherent disadvantage that with each reflection, some loss of light occurs, such loss typically being in the range of about 10%.
Another approach to efficiently coupling a light guide to a light source would be to conform the light guide to the shape of the light source outer envelope and permanently adhere the light guide to the light source. An approach illustrating the use of a cylindrical quartz rod fused to the surface of the light source can be found in U.S. Pat. No. 4,958,263 issued to Davenporr et al on Sep. 18, 1990 and assigned to the same assignee as the present invention. Though a more efficient means of coupling the light source output to the light guides than some previously taught techniques, it has been found that some light is lost by conforming the shape of the input face of the optical coupler to the surface of the light source. Furthermore, such an approach may be costly to implement in that the operation of fusing the quartz rod to a surface of the light source requires an additional manufacturing step than does the approach wherein the optical coupling device is merely positioned in proximate relation to the light source.
Still another approach to providing a light source and optical coupling arrangement aimed at achieving a high light collection efficiency can be found in U.S. Pat. No. 4,002,499 issued to R. Winston on Jan. 11, 1977. This patent provides for a three-dimensional, primarily cylindrically shaped solar energy concentrator which is more directed to the task of collecting light input rather than distributing light output and as such, emphasis is more directed to the geometry of the compound parabolic collector (CPC) than the relationships between the light source, the optical coupling device and the light distribution means such as fiber optics or other light guides. Furthermore, because of the 3-dimensional size and shape characteristics of this device, applications requiring that the light source, light coupling arrangement occupy as small a space as possible, would be precluded from consideration.